Audio Repair 101: Noise in Audio & Video Recordings
A Comprehensive Guide on Audio Repair: dealing with Noise
For the most part, our minds ignore the many things that we see and hear around us. Think of it - when was the last time you paid attention to every little sound that was going on around you? Your ears give your brain a lot of information, but it would be very distracting if we were to notice it all at once. This concept is important for understanding how noise can interfere with recordings. For example, the car driving by that you didn’t notice during recording is now annoying you during playback. This is because it was background noise at first. Now it is coming from the same speaker as your dialogue leaving your mind unable to separate the two. It was first out of focus, and now it is in the way.
Everyone in the world of audio will tell you the same thing. Removing noise from your location is always the first step in a great sounding recording. This is true for Podcasters all the way up to Sound Engineers. After removing background noise, choosing the best equipment is the next step. Then you can move to your last line of defense which is your post-production. Used well, this is where make your recording shine.
Acoustic Noise: Common sources
Now before we move on, let’s first separate noise into two different types. The first is static noise. Static noise is any noise which is constant and changes very little. Examples of this include air conditioners, busy roads, and machinery. Our other type is impulsive noise. These noises are usually unpredictable and happen without warning. A gust of wind or a bird chirping are examples of impulsive noise.
Since we now understand the differences between the two types of noise, let’s discuss how to approach them. Try this: close your eyes and pick out every sound you hear from wherever you are. It’s likely that you will pick out at least a few, some that you may have not even noticed until now. This should be the very first thing that you do whenever you enter a location that you want to use for recording. Try to focus in on what your mind wants to ignore. Hear every little sound that can ruin your work and distract your audience. Keep in mind that not all background sounds are bad sounds. For instance, you may want your audience to know that the location is hot. In this case, hearing the quiet hum of a fan will actually be helpful. This phase of the process is the determining phase. It’s the time in which you identify your sources of sound. Then you can decide if they are valuable to the recording or simply noise.
Best practices to avoid acoustic noise during audio/video recordings
With the bad sounds identified, you either try to remove them or protect your inputs from them. Removing noise can be as simple as unplugging a noisy air conditioner or turning off the dryer for a few minutes while you film. If this is all you have to do to prepare, it’s a happy day, but what happens when you can’t stop the noise? Is stopping traffic on the nearby highway the most practical way to control the noise? It’s times like these where dampening the sound is your next best option.
To create an environment that dampens noise, you have to add materials that absorb sound. Sounds tend to bounce off of flat, hard surfaces. If your location is an empty room with bare walls and hardwood floors, you can cover the area off-screen with blankets and rugs. Taking measures to dampen sound can bring out the clarity of the good audio you intend to capture.
Watch here how to make DIY Sound Absorption Panels
A small lavalier microphone hidden near your subject’s mouth will enable you to turn the gain down low. This is because you are already picking up so much volume due to the proximity. By doing this, the microphone will not pick up as much of the ambient noise of the environment. Lavalier microphones are small and easy to hide within clothing or even hair. Other than their small size, lavalier microphones do not differ much from other microphones. They can be produced in all the same varieties that you would find among other, less versatile styles of microphones.
Along with the lavalier, a boom microphone will go a long way to adding balance to your recording. This is because it’s always placed off screen at a more natural distance from the subject or point of interest. This opposes the placement of the lavalier, which is near the subject's mouth. In your final mix, the lavalier will ultimately play a supporting role to the audio captured by the boom. Its purpose is to provide a little extra volume and clarity to the dialogue. A lavalier placed within clothing is safe from wind. How, then, is the boom protected when it’s dangling out in the open? Since it’s never going to be on screen, its wind filter is free to be large and a little strange looking for the sake of protection. Remember, sound and wind are two different things. Wind is the movement of air, while sound is its vibration. The big, fuzzy wind filters only stop the flow of air from reaching the microphone. They still allow the vibrations to pass through.
Electrical Noise: Common sources
When what goes on outside of your recording equipment has been dealt with, it’s time to turn inward. Microphones capture sound much the same way as our own ears. The diaphragm vibrates along with the air around it. Then it converts the vibrations into an electrical signal which perfectly represents the sound. By doing so, our new form of energy is now open to a whole new set of interference sources. Wifi, cell phone networks, and radio waves can all disrupt electrical signals. To prevent this from happening, we need to have a basic understanding of grounding. This, in turn, will help us to choose the best equipment for each job.
Keep in mind, this conversation can quickly become very complicated and painful to the brain. So, for those of you who are into that sort of thing, I invite you to investigate further. For our purposes, we will only skim the surface of electrical grounding. Examine the audio cables you have. There are many different kinds, but they all fall into one of two categories. Whether it’s an RCA, ¼” TRS, 1/8” TRS, or XLR; they all have either two conductors or three. Each one of these conductors has a specific purpose. In the case of the two conductor connectors, one is for transmitting signal while the other is the ground. This type of connection is known as an unbalanced connection. If you plug one of these cables into an amplifier only halfway, there will be a very loud buzz. That's because the ground has not yet made contact. Doing this gives you an idea of how important grounding is. The ground only provides so much protection for your signal, however. If your unbalanced cable is longer than 15 feet (or 5 meters), the signal will become too full of noise. This is because more copper means more room for interference.
Best practices to avoid electric noise during audio/video recordings
This is where balanced connections become a lifesaver. These connectors have three conductors instead of two. Two of the conductors transmit signal, and the third conductor is the ground. Without getting too technical, the two signals cancel each other out leaving the interference behind. Your audio equipment can then remove this interference and keep the good signal. This method, along with the grounding, allows these cables to reach up to between 100 to 150 feet (or 45 meters) depending on who you ask. If you can, use balanced cables like the XLR or ¼” TRS to keep your audio as clean as possible. As a side note, don’t be fooled by the three conductors on your headphone jack. Those are a pair of unbalanced signals to give you your left and right stereo pair with a ground. It is not a mono balanced connection like the other three conductor connectors. Moving on!
A good practice no matter what kind of cable you are using is to keep them at least one or two feet away from power cords. Cords with a lot of electricity flowing through them have strong energy fields around them. These fields, if left close to your signal cable, can overpower your signal with noise. If you have followed all this and still hear a buzz, there may be a grounding problem inside your equipment. This is rare, but it does happen from time to time.
We’ve covered a lot of ground at this point. Now you should have basic knowledge on how to cut noise from the environment and the equipment. If you have gone through both of these steps and still have noise, there is still hope. This is where we move on to the post-production phase. The best advice I can give you for this part is this: some audio will never sound good no matter what you do in post- production. That is why this is the last step. The tools that are out there are not intended to clean up messes, but rather to polish a track that is already good. This process requires finesse, not brute force.
If you still have a slight hum, harsh sibilance (the “s” sound), or loud plosives (“b” or “p” sounds), then there are a few options out there for removing these from your recording. Most people are familiar with Audacity. This program is free and comes with many audio editing tools that can work great for these scenarios. Yet, using these tools requires a good ear and knowledge of audio. An experienced sound engineer can listen to the hum on a track and tell you it’s 300Hz. Then they will notch it out with an EQ in a matter of no time. Or, in the case of a high-pitched hiss, they could run the track through a low-pass filter.
How to restore noisy audio recordings
How to Remove Noise with Audacity
Trying to remove noise with Audacity can be a challenging process. Below, we have tested three different ways of noise removing, Audacity's Noise Reduction tool, Audacity's Equalization & ERA Noise Remover.
Original sample with noise:
Audacity's Noise Reduction
After locating and opening Audacity's Noise Reduction, we have to click on "Get Noise Profile" and let our sample play.
Then, re-opening Noise Reduction, we can adjust the settings to get the best result possible.
Even after applying Noise Reduction, we can see from the waveform that the noise wasn't fully removed. Listen to the sample after this process:
Cut out the noise with EQ:
Another way to deal with noisy audio, could be by applying EQ on it and cut out some frequencies. To do so, we have to open Equalization effect, and cut off some frequencies. In some cases, like our sample's one, the frequency range of the noise is wide enough so the process will affect the voice's frequencies as well.
Listen to the sample after applying Equalization.
ERA Noise Remover:
If that sounds foreign to you, you may want to consider a tool that will take out some of the guess work. The ERA Bundle by Accusonus provides software plugins that target the most common audio problems. I, myself, have spent hours fumbling with EQ’s and other tools. When I was first starting out, it was hard to achieve the effect that these plugins have at the press of a button.
If we look at the waveform after the process, we can see that the noise is totally removed. Listen to the final result: